JP Publication of Application No. 2011-116313 describes an article transport vehicle comprising travel members configured to travel along travel rails, a support member located below the travel members for supporting an article, and connecting members for connecting the travel members and the support member to each other.
In this article transport vehicle, when there is a step in a travel rail and a vertical vibration or jolt occurs as the vehicle travels over the step, the vibration can be easily transmitted to the support member and, in turn, to the article through the connecting members. When the vibration of the travel members is transmitted to the article supported by the support member, the article may be damaged by the vibration. Therefore, it is desirable to reduce any vertical vibration that is transmitted to the article when a travel member travels over a step in a travel rail.
Incidentally, each travel member of the article transport vehicle described in the aforementioned patent has driven wheels which roll on the travel surfaces of the travel rails, and an electric motor which drivingly rotates the driven wheels. Since the space between the driven wheels and the electric motor is small, it is not easy to provide a mechanism for absorbing vertical vibration, between the driven wheels and the electric motor. In addition, the support member of the article transport vehicle described in the aforementioned patent is provided with a gripper. And the support member is configured to support an article with the article suspended therefrom by inserting the gripper under a flange formed in the upper end portion of the article. Since the space under the flange is also small, it is not easy to provide the gripper with a mechanism for absorbing vertical vibration.